Basically this means that your 3750X does not have a valid IOS to boot from. The 3750X is a wee bit smart: If you have the wrong boot variable it will go and look for a valid IOS BIN file until there is none. This is what is happening to you.
Now there are two ways to solve this issue: The easy way or the hard way
The hard-way is to follow Cisco's documentation and boot from ROMmon.
1. set BAUD 115200 (this enables you to speed up the process from 4 hours to 50 minutes);
2. Change your terminal baud rate to 115200;
3. copy xmodem flash:
4. UPLOAD option based on the terminal emulator software you are using.
5. When done, undo the high-baud rate with the command "unset BAUD"
The easy-way. The 3750E/3750X has a USB port. This USB port can be used to enable the 3750X to boot a valid IOS from the USB port.
1. NOT ALL USB STICKS ARE SUPPORTED;
2. Format the USB stick with FAT16 before putting an IOS in it;
3. Copy the BIN file into the USB stick;
4. Command to boot the appliance from ROMmon using the USB stick: boot usbflash0:filename.bin
Hope this works.
